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Caribbean fish biodiversity shown to be linked to sea temperature


A study published today in the Journal of Biogeography has utilised citizen science to produce a new map of marine fish biodiversity across the Caribbean and beyond.

The work, performed by scientists from Plymouth’s Marine Biological Association and Denmark’s Center for Macroecology, Evolution & Climate, studied a huge database collected by volunteer SCUBA diving enthusiasts to produce the map, and found fish biodiversity to be strongly linked to sea temperatures. However, while fish biodiversity is higher in warmer waters, the very hottest sites in fact have fewer species than sites with intermediate temperatures, something not shown before in previous studies. These results will be of concern given the rapidly rising water temperatures in the region.

This ground-breaking research is based on data collected by thousands of marine citizen scientists working within the Reef Environmental Education Foundation’s (REEF) SCUBA diving-based fish survey project. These volunteers have been recording data on the fish species they see during dives for over 25 years and inputting their records into REEF database. This huge volunteer effort has enabled researchers to compare different hundreds of coral reefs and other coastal sites across this tropical region. The resulting map shows high diversity areas in the Dutch Antilles and the Florida Keys, whereas relatively few species were found areas such as Bermuda, the Gulf of Mexico and Northern Florida.

In order to examine potential explanations for these patterns, the research team looked at potential environmental factors that might be associated with them, including natural factors, such as temperature, salinity and depth, and human-based factors, such as population density. Analysis proved the number of fish species recorded at a site could be predicted by how warm the water was at that site and, to a lesser extent, how deep the site was. While a positive relationship between temperature and biodiversity has been demonstrated in previous research of global patterns, the fine scale detail provided by this huge citizen science data set facilitated the discovery of important details of this relationship within tropical region.

Senior author Dr Ben Holt said: "Rather than being a simple relationship, whereby warmer waters lead to more fish species, the relationship seen in the REEF data was “hump-shaped”; warmer sites tend to have more species only up to an optimal temperature of around 27oC and then the very hottest sites are less diverse.”

Further analysis suggests that this result may be partly driven by a fewer species being adapted to the warmest temperatures. The findings of this study will inevitably be of concern given the fast rising temperatures of Caribbean water but the research team urge caution extrapolating their results based on future climate predictions.

Dr Holt added: “The efforts of citizen scientists have provided an invaluable opportunity to study spatial patterns of marine biodiversity. These results do not necessarily directly transfer to changes over time at any particular site, for example as seawater temperatures change in the future. This is an important area for further research given the importance of these habitats within the Caribbean and around the world.”